Semiconductor module and method for manufacturing semiconductor module

ABSTRACT

A semiconductor module includes a first metal foil; an insulating sheet mounted on a top surface of the first metal foil; at least one second metal foil mounted on a top surface of the insulating sheet; at least one semiconductor device mounted on the second metal foil; and a resin case for surrounding the first metal foil, insulating sheet, second metal foil, and semiconductor device. A bottom end of a peripheral wall of the resin case is located above a bottom surface of the first metal foil. A resin is provided inside the resin case to fill the inside of the resin case. The bottom surface of the first metal foil and the resin form a flat bottom surface so that the flat bottom surface contacts an external mounting member.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

This invention relates to a semiconductor module and a method for manufacturing a semiconductor module, and in particular relates to a semiconductor module mounted with a power semiconductor device, and a method for manufacturing such a semiconductor module.

In inverter devices, uninterruptible power supply devices, machining equipments, industrial robots, and other equipments, semiconductor modules, which are independent of the main unit of the equipment, are employed.

As the construction of such semiconductor modules, generally, a metal base plate of prescribed thickness is used as a foundation, and a package mounted with power semiconductor devices is provided on the metal base plate (see for example Japanese Unexamined Patent Publication No. 2003-289130). For example, FIG. 7 is a schematic diagram of a semiconductor module employing a metal base plate as a foundation.

This semiconductor module 100 employs a metal base plate 101 with several millimeters in thickness as a foundation. Metal foil 103 is mounted onto the metal base plate 101 through a solder layer 102. An insulating sheet 104 is mounted onto the metal foil 103. And metal foils 105, 106 are mounted onto the insulating sheet 104. Further, on the metal foils 105, 106 are mounted semiconductor devices 109, 110, through solder layers 107, 108. Here, the semiconductor devices 109, 110 are, for example, IGBTs (Insulated Gate Bipolar Transistors), FWDs (Free Wheeling Diodes), or other devices. And, onto the semiconductor devices 109, 110 are mounted heat spreaders 113, 114, through solder layers 111, 112. A resin case 115, molded so as to surround the semiconductor devices 109, 110 and the like, is fixed onto the upper edge of the metal base plate 101.

Although not shown, metal wires, lead frames, and similar are arranged on the periphery of the semiconductor devices 109 and 110; for example, electrodes of the semiconductor devices 109, 110 are electrically mounted to a circuit pattern formed on the insulating sheet 104, or, electrical connections are formed between electrodes of the semiconductor devices 109, 110.

Further, the interior of the resin case 115 is filled with a gel 116, in order to prevent contact between metal wires and similar, and to protect the semiconductor devices 109, 110, and similar from moisture, humidity, and dust.

A cooling member 130 is positioned below the semiconductor module 100, bolts or similar are passed through holes 117 provided in the resin case 115 and metal base plate 101, and the metal base plate 101 is brought into close contact with the cooling member 130 by tightening the bolts or similar.

There are cases in which the resin case 115 is damaged in the vicinity of the holes 117 by tightening the bolts or similar. In order to prevent such damage, reinforcing metal rings 118 are provided on the inside of the holes 117 in the resin case 115.

However, such a semiconductor module 100 employs a thick metal base plate 101 as a foundation, so that the weight and size of the semiconductor module cannot be decreased.

Hence, there has been disclosed a small-size semiconductor module which does not use a metal base plate 101 as a foundation (see for example Komatsu, Saotome and Igawa, “Small-capacitance IGBT module”, Fuji Jihou, Vol. 78, No. 4, 2005, pp. 260-263).

FIG. 8 is a schematic diagram of a semiconductor module which does not use a metal base plate.

This semiconductor module 200 is based on an insulating sheet 104, metal foil 103 formed below the insulating sheet 104, and metal foils 105, 106 formed above the insulating sheet 104. Onto the metal foils 105, 106 are mounted semiconductor devices 109, 110, through solder layers 107, 108. In this type of semiconductor module 200, a resin case 115, molded so as to surround the semiconductor devices 109, 110, is fixed onto the upper edge of the insulating sheet 104. The interior of the resin case 115 is similarly filled with a gel 116 comprising a silicone material.

By means of such a semiconductor module 200, a thick metal base plate needs not be used as a foundation, so that the semiconductor module can be made lighter and more compact, and costs can be reduced.

Further, in a semiconductor module 200 of this type where there is no metal base plate, a metal hook 119 for installation is separately provided on a side portion of the resin case 115. A bolt or similar penetrates the metal hook 119, and the semiconductor module 200 is fixed to the cooling member 130 by tightening the bolt or similar.

However, in the construction of a semiconductor module 200 shown in FIG. 8, a soft gel 116, comprising a silicone material, is used as the sealing material in the resin case 115.

When a bolt is used to firmly fasten the semiconductor module 200 sealed with such a gel 116 on the cooling member 130, excessive amount of stress is applied to the insulating sheet 104 within the semiconductor module 200, and in some cases the insulating sheet 104 is damaged. That is, because the gel 116 is soft, deformation (distortion) of the insulating sheet 104 cannot be avoided. As a result, the insulating sheet 104 is damaged.

In order to avoid such damage, the semiconductor module 200 must be fastened to the cooling member 130 in such a range that there is no damage to the insulating sheet 104. Hence, in this structure of a semiconductor module 200, the metal foil 103 cannot be firmly brought into close contact with the cooling member 130. As a result, there has been a problem that an adequate cooling effect cannot be obtained.

Moreover, in the semiconductor module 200, heat is dissipated each time the semiconductor devices 109, 110 are operated, and this heat also causes deformation of the insulating sheet 104. Hence, as the semiconductor module 200 is used over a long period of time, deformation of the insulating sheet 104 repeatedly occurs. As a result, there has been a problem that the solder layers 107, 108 immediately below the semiconductor devices 109, 110 peel away.

Further, in such a semiconductor module 200, the thickness of the insulating sheet 104 is increased in order to secure adequate mechanical strength (for example, approximately 0.6 mmt or greater).

However, in a semiconductor module 200 using such a thick insulating sheet 104, there is a limit as to the thermal conductivity from the lower faces of the semiconductor devices 109, 110 to the cooling member 130. For this reason, there has been a problem that high-power semiconductor devices could not be incorporated into such semiconductor modules 200.

Also, this structure for a semiconductor module 200 necessitates the additional manufacturing step of separately installing a metal hook 119 for installation of the resin case 115.

This invention has been made in light of the above problems, and has objectives to provide a semiconductor module which achieves reduced weight, smaller size, and lower cost for mounting with high-power semiconductor devices and has an adequate cooling effect, and a method for manufacturing a semiconductor module.

Further objects and advantages of the invention will be apparent from the following description of the invention.

SUMMARY OF THE INVENTION

In order to achieve the objectives stated above, the invention provides a semiconductor module comprising an insulating sheet; a first metal foil mounted to a first main face of the insulating sheet; at least one second metal foil mounted to a second main face of the insulating sheet; at least one semiconductor device mounted onto the second metal foil; a resin case which surrounds the first metal foil, insulating sheet, second metal foil, and semiconductor device above the lower face of the first metal foil; and resin which is filled into the space between the inner surface of the resin case and the outer peripheral-edge face of the first metal foil and the outer faces of the insulating sheet, second metal foil, and semiconductor device. A flat face, which can be brought into close contact with an external mounting member, is formed by the lower face of the first metal foil and the resin exposed from the resin case.

Further, this invention provides a method for manufacturing a semiconductor module. The method includes the steps of: preparing a board having an insulating sheet, a first metal foil mounted to a first main face of the insulating sheet, and at least one second metal foil mounted to a second main face of the insulating sheet; mounting at least one semiconductor device on the second metal foil; placing a resin case which surrounds the first metal foil, insulating sheet, second metal foil, and semiconductor device above the lower face of the first metal foil, onto the board; pouring resin in paste form into the space between the inner face of the resin case and the outer peripheral-edge face of the first metal foil and the outer faces of the insulating sheet, second metal foil, and semiconductor device; and heat-curing the resin, wherein a flat face, which can be brought into close contact with an external mounting member, is formed by the lower face of the first metal foil and the resin exposed from the resin case.

According to the semiconductor module and method for manufacturing the semiconductor module, the first metal foil is mounted to the first main face of the insulating sheet, at least one second metal foil is mounted to the second main face of the insulating sheet, and at least one semiconductor device is mounted onto the second metal foil. And, the first metal foil, insulating sheet, second metal foil, and semiconductor device are surrounded by a resin case above the lower face of the first metal foil. The space between the inner face of the resin case and the outer peripheral-edge face of the first metal foil and the outer faces of the insulating sheet, second metal foil, and semiconductor device is filled with resin. And, a flat face is formed which can be brought into close contact with an external mounting member by the lower face of the first metal foil and the resin exposed from the resin case.

In a semiconductor module and a method for manufacturing a semiconductor module of this invention, a first metal foil is mounted to a first main face of an insulating sheet, at least one second metal foil is mounted to a second main face of the insulating sheet, and at least one semiconductor device is mounted onto the second metal foil. And, a resin case surrounds the first metal foil, insulating sheet, second metal foil, and semiconductor device above the lower face of the first metal foil, and resin is filled into the space between the inner face of the resin case and the outer peripheral-edge face of the first metal foil and the outer faces of the insulating sheet, second metal foil, and semiconductor device. Moreover, a flat face is formed which can be brought into close contact with an external mounting member by the lower face of the first metal foil and the resin exposed from the resin case.

By this means, a semiconductor module and a method for manufacturing a semiconductor module can be made such that the semiconductor module mounted with power semiconductor devices is light in weight, small in size, and low in cost, has an adequate cooling effect, and can be mounted with high-power semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A), 1(B), 1(C) are schematic diagrams of principal portions, explaining the configuration of a semiconductor module;

FIG. 2 is a first diagram explaining a process in a semiconductor module manufacturing method;

FIG. 3 is a second diagram explaining a process in a semiconductor module manufacturing method;

FIG. 4 is a third diagram explaining a process in a semiconductor module manufacturing method;

FIG. 5 explains the structure of a board deformed into a convex shape;

FIG. 6 is a schematic diagram of a cross-section of principal portions, explaining a modified example of a semiconductor module;

FIG. 7 is a schematic diagram of a conventional semiconductor module employing a metal base plate as the foundation; and

FIG. 8 is a schematic diagram of a conventional semiconductor module not employing a metal base plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, the invention is explained in detail, referring to the drawings.

First, the configuration of a semiconductor module is explained.

FIGS. 1(A), 1(B), 1(C) are schematic diagrams of principal portions, explaining the configuration of a semiconductor module. Here, in FIG. 1(A), a schematic top view of principal portions of a semiconductor module 1 is shown, and in FIG. 1(B), a schematic diagram of a cross-section of principal portions of the semiconductor module 1 is shown. In FIG. 1(C), a schematic bottom view of principal portions of the semiconductor module 1 is shown.

Also, in FIG. 1(B), a cross-sectional view taken along a line 1(B)-1(B) in FIGS. 1(A) and 1(C) is shown. In FIGS. 1(A), 1(B), a state is shown in which a cooling member 40 (cooling fins), which is the external mounting member, is mounted to the lower face of the semiconductor module 1. In FIG. 1(C), however, the cooling member 40 is not shown in order to clearly display the lower face of the semiconductor module 1.

In the semiconductor module 1 shown, a board is formed of a rectangular insulating sheet 10, metal foil 11 formed by a DCB (Direct Copper Bonding) method on the lower face of the insulating sheet 10, and at least one other metal foil 12 (in FIG. 1, two metal foils 12) formed by the same DCB method on the upper face of the insulating sheet 10. At Semiconductor devices 14, 15 are mounted onto the metal foils 12 with a tin (Sn)-silver (Ag)-based lead-free solder layer 13 intervening. Here, the insulating sheet 10 is, for example, formed from an alumina (Al₂O₃) sintered ceramic, and the metal foils 11, 12 are formed from metal whose main component is copper (Cu). The semiconductor devices 14, 15 are for example IGBT devices, FWD devices, power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), or other power semiconductor devices.

Further, heat spreaders 16, whose main component is copper, are mounted, via a solder layer 17 of the same component, onto the surface electrodes (not shown) arranged on the upper faces of the semiconductor devices 14, 15.

In the semiconductor module 1, an insulating sheet with thickness approximately 0.35 mmt or less is used as the insulating sheet 10 in order to shorten the heat dissipation path from the lower faces of the semiconductor devices 14, 15 to the upper face of the cooling member 40. Further, the thickness of the metal foils 11, 12 mounted to the main faces of the insulating sheet 10 is thicker than that of the metal foils 103, 105, 106 shown in FIG. 7 and FIG. 8, for example, 0.5 to 0.6 mm.

In FIGS. 1(A), 1(B), 1(C), particularly, although not shown, a plurality of semiconductor devices other than the semiconductor devices 14, 15 (for example, IGBT devices, FWD devices, power MOSFETs, and similar) is mounted on the insulating sheet 10, and in addition to the metal foils 12, a plurality of electrode terminals and similar is arranged on the insulating sheet 10. On the periphery of the semiconductor devices 14, 15 are arranged metal wires, lead frames, and similar, to electrically connect, for example, the electrodes of the semiconductor devices 14, 15 and respective metal foils, or to connect the electrodes of the semiconductor devices 14, 15 to each other using metal wires.

Further, a molded resin case 20 is provided on the semiconductor module 1, so as to surround the metal foil 11, insulating sheet 10, metal foils 12, semiconductor devices 14, 15, and heat spreader 16, above the lower face 11 a of the metal foil 11.

Here, the material of the resin case 20 is, for example, PPS (polyphenylene sulfide). Further, fastening portions 20 a for bolting are provided on a side portion of the resin case 20 so as to enable installation of the semiconductor module 1 on the cooling member 40. The fastening portions 20 a are integrally molded with the resin case 20, and extend outward from side faces of the resin case 20.

A highly rigid epoxy resin 30 is filled (sealed) into the space between the inner face of the resin case 20 and the outer peripheral-edge face of the metal foil 11 and the outer faces of the insulating sheet 10, metal foils 12, semiconductor devices 14, 15, and heat spreader 16. However, the lower face of the metal foil 11 is exposed from the epoxy resin 30.

This epoxy resin 30 is poured into a resin-inflow opening 20 b provided in the center of the upper face of the resin case 20, to seal the semiconductor devices 14, 15, insulating sheet 10, and similar (details are explained below). Further, the epoxy resin 30 is filled so as to enter into the interior of the fastening portions 20 a. Holes 21, through which bolts or other screw portions are to be passed, are formed penetrating the fastening portions 20 a and the epoxy resin 30 inside the fastening portions 20 a.

The epoxy resin 30 is filled up to the same height as the lower face 11 a of the metal foil 11. And, a broad flat face 22 is formed by an outer face 30 a formed by epoxy resin 30 exposed from the resin case 20 and the lower face 11 a of the metal foil 11. That is, the flat face 22, in which the outer face 30 a of epoxy resin 30 is combined with the lower face 11 a of the metal foil 11, becomes the bottom face of the semiconductor module 1. By providing this flat face 22, the semiconductor module 1 can be brought into firm and close contact with the cooling member 40 at the bottom face. The above-described epoxy resin 30 comprises an inorganic filler, which is not shown.

Further, in the semiconductor module 1, the thermal expansion coefficient of the epoxy resin 30 is adjusted so as to match, as much as possible, the thermal expansion coefficients of the metal foils 11, 12. For example, if the thermal expansion coefficient of the metal foils 11, 12, formed from copper is approximately 16.5 ppm/K, then the thermal expansion coefficient of the epoxy resin 30 filled into the resin case 20 is approximately 15 ppm/K. By this means, when, for example, the semiconductor module 1 is operating, even if expansion and contraction of the metal foils 11, 12 occur, there is no occurrence of local stresses on the insulating sheet 10 or on the semiconductor devices 14, 15 because the thermal expansion coefficients are matched.

Also, whereas the thermal conductivity of the silicone gel used in the past as a sealing material is approximately 0.3 W/mK, the thermal conductivity of the epoxy resin 30 filled into the resin case 20 is adjusted to approximately 1 W/mK. Hence, heat generated by the semiconductor devices 14, 15 in the semiconductor module 1 is dissipated on the side of the cooling member 40, and is also dissipated on the side of the epoxy resin 30. As a result, heat generated by the semiconductor devices 14, 15 is dispersed above the semiconductor module 1 and in lateral directions, and so the semiconductor module 1 has a greater cooling effect.

The semiconductor module 1 is mounted to the cooling member 40 by passing bolts or similar through the holes 21 and fixing to the cooling member 40.

In order to further promote the cooling effect, a thermal compound (not shown) or similar may be applied between the bottom face of the semiconductor module 1 and the upper face of the cooling member 40.

By means of this construction of the semiconductor module 1, the outer faces of the insulating sheet 10, metal foils 11, 12, and semiconductor devices 14, 15 are backed by highly rigid epoxy resin 30.

Specifically, a highly rigid epoxy resin 30 is filled into the space between the inner face of the resin case 20 and the outer peripheral-edge face of the metal foil 11 and the outer faces of the insulating sheet 10, metal foils 12, and semiconductor devices 14, 15. And, a broad flat face 22 is formed by means of an outer face 30 a formed of epoxy resin 30 exposed from the resin case 20 and the lower face 11 a of the metal foil 11. Further, this flat face 22 is brought into contact with the upper face of the cooling member 40.

A fastening portion 20 a, integrally formed with the resin case 20, extends from a side face of the resin case 20, and the interiors of the fastening portions 20 a are also filled with highly rigid epoxy resin 30.

By means of this construction of the semiconductor module 1, by passing bolts or similar through the holes 21 provided in a side portion of the resin case 20, the entirety of the semiconductor module 1 can be firmly fastened by the bolt or similar to the cooling member 40. And, by means of this firm fastening, the flat face 22 and the upper face of the cooling member 40 can be brought into firm and close contact. As a result, a greater cooling effect can be secured for the semiconductor module 1.

Because a broad flat face 22 is formed on the semiconductor module 1, even when the entirety of the semiconductor module 1 is firmly fastened to the cooling member 40 by means of a bolt or similar, the contact pressure is uniformly distributed over the flat face 22. As a result, even when the entirety of the semiconductor module 1 is firmly fastened to the cooling member 40 by means of a bolt or similar, there is no occurrence of local stresses in the insulating sheet 10, deformation of the insulating sheet 10 is suppressed, and damage to the insulating sheet 10 is prevented.

Also, even when heat generated during operation of the semiconductor devices 14, 15 would cause deformation of the insulating sheet 10, deformation of the insulating sheet 10 during operation of the semiconductor devices 14, 15 is suppressed, and damage to the insulating sheet 10 is prevented because stresses occurring within the insulating sheet 10 are distributed within the epoxy resin 30 as described above.

Further, peeling and similar of the solder layer 13 immediately below the semiconductor devices 14, 15 can also be prevented because deformation of the insulating sheet 10 is suppressed.

The interiors of the fastening portions 20 a are filled with the highly rigid epoxy resin 30, and the strength thereof is reinforced. Hence, even when bolts or similar are directly passed through the holes 21 and firmly tightened, damage to the fastening portions 20 a does not occur. For this reason, there is no need to provide a metal ring 118 on the inside of the holes 21 for reinforcement, as shown in FIG. 7.

In the semiconductor module 1, a thick metal base plate 101 is not used as in the case of the semiconductor module 200 shown in FIG. 7. As a result, the semiconductor module can be made lighter and more compact, and costs can be reduced.

In the semiconductor module 1, an insulating sheet 10, which is thinner than in the semiconductor module 200 shown in FIG. 8, is used, and still thinner metal foils 11, 12 are used. Hence, a greater cooling effect is obtained in the case of the semiconductor module 1 than the semiconductor module 200. As a result, the semiconductor devices 14, 15 in the semiconductor module 1 can operate with greater stability.

Further, because the cooling effect of the semiconductor module 1 is enhanced, it is possible to mount a semiconductor more powerful, compared to the semiconductor module 200.

Specifically, comparing the structure of PIMs (Power Integrated Modules) configured in the circuitry of inverters, converters and brakes, and structures (6-in-1 structures) where six pairs of IGBTs and FWDs connected in parallel in inverter circuits are combined in one package, the structure of a semiconductor module 200 enables mounting of semiconductor devices with a current rating at 1200 V of up to 15 A in the case of a PIM structure, and a current rating at 1200 V of up to 35 A in the case of a 6-in-1 structure. Whereas, when employing the structure of the semiconductor module 1, semiconductor devices can be mounted with a current rating at 1200 V of up to 35 A in the case of a PIM structure, and with a current rating at 1200 V of up to 50 A in the case of a 6-in-1 structure.

Further, in the semiconductor module 1, holes 21 with high rigidity are provided in a side portion of the resin case 20, so that there is no need to separately provide a metal hook 119 for protection, as in the semiconductor module 200 shown in FIG. 8. As a result, semiconductor module manufacturing processes can be shortened, and costs can be reduced.

Next, a method for manufacturing the semiconductor module 1 is explained. In the following drawings, members which are the same as in FIGS. 1(A), 1(B), 1(C) are assigned with the same symbols, and detailed explanations thereof are omitted.

FIG. 2 is used to explain one process in the method for manufacturing a semiconductor module.

First, as shown in FIG. 2, a board 50 is prepared in such a way that at least one metal foil 12 is mounted by the DCB method onto an insulating sheet 10. Then, the semiconductor devices 14, 15 are mounted onto the metal foil 12 through a solder layer (not shown). Here, the material of the metal foil 12 includes copper, for example, as the main component, and is for example 0.5 to 0.6 mm thick. Then, a heat spreader 16 is mounted onto each of the main electrodes of the semiconductor devices 14, 15 through a solder layer (not shown). The heat spreaders 16 are electrically connected to the metal foils 12 by metal wires 18.

Patterned metal foil (copper of thickness 0.5 to 0.6 mm) is mounted to the lower face of the insulating sheet 10 in the board 50 by the DCB method, but this metal foil is not shown in the figure.

In FIG. 2, a lid portion 20 c forming the upper lid of the resin case 20 is shown. A plurality of lead frames 23 for external connection terminals is arranged in advance so as to penetrate the main face of the lid portion 20 c substantially in the direction perpendicular thereto.

After performing positioning of the lid portion 20 c relative to the board 50, the lid portion 20 c is moved in the direction of the arrow, to place the lid portion 20 c onto the board 50 from above the board 50.

FIG. 3 explains one process in the method for manufacturing the semiconductor module.

As shown in FIG. 3, as a result of placing the lid portion 20 c on the board 50, the plurality of lead frames 23 and the plurality of metal foils 12 on the board 50 are in contact. The portions to be in contact are soldered, so that the lead frames 23 are electrically connected to the respective metal foils 12. By mounting the lead frames 23 onto the respective metal foils 12, the lid portion 20 c is fixed onto the board 50.

Next, as shown in FIG. 3, the outer frame portion 20 d which forms a large portion of the resin case 20 is positioned above the board 50 and lid portion 20 c. As stated above, this outer frame portion 20 d has fastening portions 20 a on the sides which are integrally formed.

Then, the outer frame portion 20 d is moved in the direction of the arrow toward the board 50, and the outer frame portion 20 d is mated with the board 50 and lid portion 20 c from above.

FIG. 4 explains one process in the method for manufacturing the semiconductor module.

In FIG. 4, a state where the outer frame portion 20 d is mated with the board 50 and lid portion 20 c is shown. In this state, on the side above the lower face of the metal foil, not shown, mounted to the lower face of the insulating sheet 10, the metal foil, insulating sheet 10, metal foils 12, semiconductor devices 14, 15, and heat spreaders 16 are surrounded by the resin case 20 (lid portion 20 c, outer frame portion 20 d).

Then, the mated member 51 is sandwiched between a lower jig 60 and upper jig 61 for molding, as shown in FIG. 4, and a heat-curing type epoxy resin 31 is poured into a resin-inflow opening 20 b provided in the center of the lid portion 20 c. At this stage, the epoxy resin 31 is in paste form.

When the epoxy resin 31 is poured into the resin-inflow opening 20 b, the epoxy resin 31 flows into the space between the inner face of the resin case 20 and the outer peripheral-edge face of the metal foil 11 and the outer faces of the insulating sheet 10, metal foils 12, and semiconductor devices 14, 15, as well as the heat spreaders 16. In addition, the epoxy resin 31 is filled in the fastening portions 20 a. The inner face 60 a of the lower jig 60, which is in contact with the lower portion of the mated member 51, forms a broad flat face wider than the mated member 51.

Then, after completely pouring the epoxy resin 31 in paste form into the resin case 20, the mated member 51 is heated for a prescribed time at the curing temperature of the epoxy resin 31.

By means of this heat treatment, the epoxy resin 31 which has been poured into the resin case 20 is cured, and the highly rigid epoxy resin 30 shown in FIG. 1 seals the space between the inner face of the resin case 20 and some of the outer faces of the semiconductor devices 14, 15, insulating sheet 10, metal foils 11, 12, and heat spreaders 16.

Further, because the inner face of the lower jig 60 in contact with the mated member 51 is a flat face, a broad and flat bottom face is formed by the main face of the metal foil 11 and epoxy resin 31 exposed from the resin case 20.

During pouring the epoxy resin 31, circular column-shape protruding portions 61 a provided on the upper jig 61 are inserted into holes formed in advance in the fastening portions 20 a, and the tips of the protruding portions 61 a are brought into contact with the lower jig 60. By this means, epoxy resin 31 does not flow into the portions where the protruding portions 61 a are positioned, and after the epoxy resin 31 is cured, the holes 21 shown in FIG. 1 are formed.

Through these manufacturing processes, the semiconductor module 1 shown in FIGS. 1(A), 1(B), 1(C) is completed.

The metal foil 11 may be structured so as to have a lower-side convex shape in the bottom face.

For example, as shown in FIG. 4, at the uppermost contact face 20 e of the resin case 20 making contact with the upper jig 61, the interior of the resin case 20 is filled with epoxy resin 31 while adjusting the force pressing on the contact face 20 e by the upper jig 61. That is, the force with which the upper jig 61 presses against the contact face 20 e is adjusted, and while causing distortion of the entirety of the mated member 51, the interior is filled with epoxy resin 31, and heat treatment is performed to cure the epoxy resin 31.

The state of a board 50 manufactured using this method is shown in FIG. 5.

FIG. 5 is used to explain the construction of a board distorted into a convex shape. In this figure, only the board 50 formed from the metal foils 11, 12 and insulating sheet 10 is shown, and other members such as the semiconductor devices 14, 15 are omitted.

As explained above, while forcibly distorting the entirety of the mated member 51, epoxy resin 31 is injected and cured to form convex-shape metal foil 11 on the lower side. The degree of warping is such that the outer edges of the metal foil 11 are distorted upwardly by 0 to 100 μm from the horizontal plane tangent at the center portion of the metal foil 11.

Immediately after placing the semiconductor module 1, provided with this convex-shape metal foil 11, on the cooling member 40, only the vicinity of the center portion of the metal foil 11 and the cooling member 40 are in contact. However, the metal foil 11 is made from metal so that it has an elasticity. Hence, by passing bolts or similar through the holes 21 positioned on side portions of the semiconductor module 1, and fastening the semiconductor module 1 to the cooling member 40 at the side portions, the contact plane between the metal foil 11 and the cooling member 40 is broadened gradually outwardly from the center portion, and ultimately the entire face of the metal foil 11 is brought into firm and close contact with the cooling member 40.

If the lower face of the metal foil 11 were deformed into a concave shape, the center portion of the metal foil 11 would not be in contact with the cooling member 40 even after fastening with bolts or similar.

By bonding such a convex-shape metal foil 11 to the semiconductor module 1, the metal foil 11 and cooling member 40 can be brought into firm and close contact, and the cooling effect of the semiconductor module 1 can be further promoted.

Finally, an example of deformation of the structure of the semiconductor module 1 is explained.

FIG. 6 is a schematic cross-sectional diagram of principal portions, explaining an example of deformation of a semiconductor module.

In the semiconductor module 2 shown in FIG. 6, at least one protruding portion 20 f is provided on the inner face of the resin case 20, in order that the resin case 20 and epoxy resin 30 may be in firm and close contact by an “anchor effect”. These protruding portions 20 f are integrally formed with the resin case 20.

By this means, even when there is some difference in the thermal expansion coefficients of the resin case 20 and epoxy resin 30, the resin case 20 and epoxy resin 30 remain reliably in close contact due to the anchor effect of the protruding portions 20 f. For example, even when the resin case 20 and epoxy resin 30 are heated due to operation of the semiconductor devices 14, 15, and there is a difference in the expansion and contraction of the resin case 20 and epoxy resin 30, due to this anchor effect, no slippage occurs at the interface between the resin case 20 and the epoxy resin 30. Further, no peeling occurs at the interface between the resin case 20 and the epoxy resin 30.

In the above, examples are explained in which the semiconductor modules 1, 2 are provided with heat spreaders 16. However, the invention is not limited to such a configuration, and heat spreaders do not have to be provided.

The disclosure of Japanese Patent Application No. 2007-132572, filed on May 18, 2007, is incorporated in the application.

While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims. 

1. A semiconductor module, comprising: a first metal foil; an insulating sheet mounted on a top surface of the first metal foil; at least one second metal foil mounted on a top surface of the insulating sheet; at least one semiconductor device mounted on the at least one second metal foil; a resin case for surrounding the first metal foil, at least one second metal foil, the insulating sheet, and the at least one semiconductor device, said resin case having a peripheral wall with a bottom end located above a bottom surface of the first metal foil; and resin filling a space inside the resin case relative to the first metal foil, at least one second metal foil, the insulating sheet and the at least one semiconductor device, wherein the bottom surface of the first metal foil and the resin form a flat bottom surface to contact an external mounting member.
 2. A semiconductor module according to claim 1, further comprising a fastening portion integrally formed with the resin case at a periphery thereof, said fastening portion being filled with the resin and having a hole penetrating the fastening portion and the resin inside the resin case.
 3. A semiconductor module according to claim 1, wherein the resin comprises an epoxy resin as a main component.
 4. A semiconductor module according to claim 1, wherein the resin case includes at least one protruding portion on an inner surface thereof.
 5. A semiconductor module according to claim 1, wherein the first metal foil has a convex portion projecting outwardly.
 6. A semiconductor module according to claim 1, wherein said first and second metal foils have thermal expansion coefficients substantially same as that of the resin inside the resin case.
 7. A semiconductor module according to claim 1, further comprising a thermal compound provided on a bottom surface of the first metal foil so that a cooling effect is enhanced.
 8. A method for manufacturing a semiconductor module, comprising the steps of: preparing a board comprising a first metal foil, an insulating sheet mounted on a top surface of the first metal foil, and at least one second metal foil mounted on a top surface of the insulating sheet; mounting at least one semiconductor device on the at least one second metal foil; placing a resin case onto the board for surrounding the first metal foil, insulating sheet, at least one second metal foil, and at least one semiconductor device, a bottom end of a peripheral wall of the resin case being located above a bottom surface of the first metal; pouring a resin in a paste form into the resin case to fill a space relative to the first metal foil, insulating sheet, at least one second metal foil and at least one semiconductor device; and heat-curing the resin, wherein the bottom surface of the first metal foil and the resin form a flat bottom surface to contact an external mounting member.
 9. A method for manufacturing a semiconductor module according to claim 8, further comprising: mounting a lid portion of the resin case having at least one lead frame on the board to contact the lead frame with the at least one second metal foil; electrically connecting the lead frame and the at least one second metal foil; and placing an outer frame portion of the resin case on the board on which the lid portion has been placed.
 10. A method for manufacturing a semiconductor module according to claim 8, wherein the first metal foil is convex toward the external mounting member after heat-curing step. 